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Plasma in the accretion disc

What is the composition of the plasma in the accretion disc? Does it include only Atoms (For example - Hydrogen) or also some other particles. If so, which kind of particles?
What is the average temp of the plasma?

Mostly electrons and cations, besides atoms. A few anions and molecules.

This might be the definition of "plasma", but the contents of an accretion disk will depend on the particular disk. Accretion disks around stellar mass black holes largely include highly ionized atoms.

What is the composition of the plasma in the accretion disc? Does it include only Atoms (For example - Hydrogen) or also some other particles. If so, which kind of particles?
What is the average temp of the plasma?

What is the composition of the plasma in the accretion disc? Does it include only Atoms (For example - Hydrogen) or also some other particles. If so, which kind of particles?
What is the average temp of the plasma?

The accretion disk temperature for non-critical systems is at most comparable to the core of the Sun, so the plasma is fairly standard. That is to say electrons and ionised atoms from the material than has fallen into it. It is not hot enough to produce exotic states of matter or much in the way of short lived particles. Some disks may reach 10^9K, which is hot but still only corresponds to an energy of 80keV or so. Which, for scale, is about the energy the first ever linear particle accelerator operated at in 1928

"This is the first time that the double-peaked line profile of this nucleus – typical of gas emission from the outer parts of an accretion disc surrounding a suppermassive black hole (SMBH) – is reported to vary. "

So we see "gas emission from the outer parts of an accretion disc surrounding a suppermassive black hole (SMBH)"

What is the composition of this gas?
Is it mainly Atoms and molecules?
Why they specifically speak about the outer part of the disc?
Is there a difference in the composition of the plasma between the outer parts of the accretion disc to the inner most?
Actually, as the SMBH is located at the center, why don't we call it accretion ring instead of disc?

Actually, as the SMBH is located at the center, why don't we call it accretion ring instead of disc?

You're just going to have to live with the fact that workers in the field develop their own terminology without consulting you, Dave. Repeatedly asking why scientists don't refer to something by the term you prefer is rather pointless and certainly a waste of time. Words and terms are invented all the time and are either accepted and gain currency, or are rejected and disappear. That's just the way it works. Scientists rejected Faraday's electrotonic but embraced anode and cathode (among others), for example. De gustibus and all that explains much.

If you're interested in etymology, consult the Oxford English Dictionary. The OED's staff are dedicated to tracing the history of words.

Actually, as the SMBH is located at the center, why don't we call it accretion ring instead of disc?

Because typically it doesn't look like a ring, it looks like a disc. The diameter of the Schwarzschild radius of a black hole (especially a stellar-mass BH) is typically orders of magnitude smaller than the accretion disc of material that forms around it.

I can't help but wonder though - if it had been called an Accretion Ring originally, would you now be demanding a response to why it was not called an Accretion Disc?

Because typically it doesn't look like a ring, it looks like a disc. The diameter of the Schwarzschild radius of a black hole (especially a stellar-mass BH) is typically orders of magnitude smaller than the accretion disc of material that forms around it.

I can't help but wonder though - if it had been called an Accretion Ring originally, would you now be demanding a response to why it was not called an Accretion Disc?

I had the impression that the plasma width in the accretion disc is quite narrow.
However, if the plasma starts almost from the diameter of the Schwarzschild radius of a black hole, and it's quite wide, than I can fully understand why we call it disc.

So, the question had to be -
What is the estimated ratio between the inwards radius to the outwards radius of the plasma in the accretion disc (in a typical spiral galaxy)?

The accretion disk temperature for non-critical systems is at most comparable to the core of the Sun, so the plasma is fairly standard. That is to say electrons and ionised atoms from the material than has fallen into it. It is not hot enough to produce exotic states of matter or much in the way of short lived particles. Some disks may reach 10^9K, which is hot but still only corresponds to an energy of 80keV or so. Which, for scale, is about the energy the first ever linear particle accelerator operated at in 1928

Edit: Changed Ionised Nuclei to Ionised Atoms

In this answer you compare the energy to the first accelerator operated at in 1928.
This is very interesting.
In the attached article (from CERN?), they discuss about the magnetic field in the accretion disc.

"Recent simulations of MHD turbulence indicate that the magneto-rotational instability efficiently generates magnetic energy in the disk"
If I understand it correctly, due to the high orbital velocity of the plasma, there is quite high magnetic energy."

So, can we assume that the accertion disc has some accelerator' characteristics as follow?

1. Very high orbital velocity - almost as high as the speed of light.
2. High Temp - ("Some disks may reach 10^9K")
3. magnetic energy - I assume that there is quite high magnetic energy in the accretion disc.

We know that the plasma is full with Hydrogen Atoms (many of them are ionized)
If so, based on the above caracteristics of the accretion disc, is there any possibility for two Hydrogen atoms to collide (during their ultra high orbital velocity) and set a new Helium atom?
If no, what kind of power/force/energy is needed in accelerator to convert two Hydrogen Atoms (ionized or unionized) into one Helium atom?

I have just found an interesting article about Plasma Power & Fusion Power

"Fusion is difficult to sustain in the lab. Since hydrogen nuclei are charged particles, they experience a strong electrostatic repulsion, which increases rapidly as the nuclei approach each other. For fusion to occur, the nuclei must hit each other at high speed, which requires a temperature of 100 million degrees. At this temperature, any contact with the container would vaporize it, so the nuclei, which are part of a plasma, must be somehow confined."

Not throughout the disk though - the edges far from the centre rotate much more slowly.

Originally Posted by Dave Lee

2. High Temp - ("Some disks may reach 10^9K")

Yes, but again only in the inner disk. The outer disk is much cooler (hence the comment about H-alpha before).

Originally Posted by Dave Lee

3. magnetic energy - I assume that there is quite high magnetic energy in the accretion disc.

Yes, but the energy in magnetic fields is not the only thing about an accelerator. It is also very much dependent on the configuration. Accelerators work by confining a beam and accelerating it, the disk magnetic fields are much less ordered.

Originally Posted by Dave Lee

We know that the plasma is full with Hydrogen Atoms (many of them are ionized)
If so, based on the above caracteristics of the accretion disc, is there any possibility for two Hydrogen atoms to collide (during their ultra high orbital velocity) and set a new Helium atom?
If no, what kind of power/force/energy is needed in accelerator to convert two Hydrogen Atoms (ionized or unionized) into one Helium atom?

A hydrogen atom has one proton, no neutrons. The formation of helium from hydrogen in stars is a multi-stage process as a helium atom consists of 2 protons and 2 neutrons. See https://en.wikipedia.org/wiki/Proton...chain_reaction for details. So while there is some scope for fusion it is unlikely to be in significant amounts due to the relatively lack of material (accretion disks are not as dense as the core of the Sun) and the difficulty of the various steps in the pp cycle.

Not throughout the disk though - the edges far from the centre rotate much more slowly.
Yes, but again only in the inner disk. The outer disk is much cooler (hence the comment about H-alpha before).
Yes, but the energy in magnetic fields is not the only thing about an accelerator. It is also very much dependent on the configuration. Accelerators work by confining a beam and accelerating it, the disk magnetic fields are much less ordered.

A hydrogen atom has one proton, no neutrons. The formation of helium from hydrogen in stars is a multi-stage process as a helium atom consists of 2 protons and 2 neutrons. See https://en.wikipedia.org/wiki/Proton...chain_reaction for details. So while there is some scope for fusion it is unlikely to be in significant amounts due to the relatively lack of material (accretion disks are not as dense as the core of the Sun) and the difficulty of the various steps in the pp cycle.

So, there is a scope for fusion but it is unlikely to be in significant amounts.
That is a very positive answer for me as I just want to understand the fesability for the Fusion process in the accertion disc.

If we compare it to the Sun;

In the following article it is stated that the Sun temp is only 10 × 10 ^ 6 °C.

"Fusion energy research uses very hot plasma. Controlled thermonuclear energy is the attempt to use plasma to get ions to a high enough energy to collide and fuse. When their nuclei fuse, a large amount of energy is released. We all know of the large energy release associated with hydrogen bombs, which fuse light atoms and thus the fusion process was created on earth and sought to be controlled. Scientists are studying ways to harness this energy release in a controlled and safe manner. These high-energy plasmas have very high temperatures that are greater than 300 × 10 ^6°C. (The temperature of the sun is on the order of 10 × 10 ^ 6 °C.) Magnetic fields contain the plasma (remember, an ionized gas is trapped by a magnetic field line), “holding” the plasma away from the vacuum chamber walls. Electromagnetic waves and ion beams are used to heat this plasma to high enough temperatures to get the ions to collide with enough energy that they will fuse. "

So, based on Hydrogen to Helium Fusion energy at the Sun, its temp had been set to 10 × 10 ^ 6 °C.
Hence, technically, if there was a similar fusion activity at the inner side of the accretion disc, don't you think that it was expected to get a similar temp as it is at the Sun?
However, the temp at the accretion disc is much higher than the Sun. (10^9K)
How can we explain that supper high temp?
If it isn't due to Hydrogen to helium fusion energy, what kind of activity/fusion can generate so high temp at the accretion disc - even for low amount? (Could it be higher level of atom -as Iron, or Molecular?)

So, based on Hydrogen to Helium Fusion energy at the Sun, its temp had been set to 10 × 10 ^ 6 °C.
Hence, technically, if there was a similar fusion activity at the inner side of the accretion disc, don't you think that it was expected to get a similar temp as it is at the Sun?
However, the temp at the accretion disc is much higher than the Sun. (10^9K)
How can we explain that supper high temp?
If it isn't due to Hydrogen to helium fusion energy, what kind of activity/fusion can generate so high temp at the accretion disc - even for low amount? (Could it be higher level of atom -as Iron, or Molecular?)

Accretion disks are not dense enough to sustain fusion at those temperatures. I'm not aware of anyone who thinks that accretion disks are fusion powered. The answer to the temperature question is in the review document I posted or on Wikipedia, if you want details. It is due to gravitational and frictional effects and our models of these effects (plus some MHD) are pretty good at explaining what we see (although, as ever, they are not perfect). Fusion of iron won't do it - in fact fusing iron takes energy, it doesn't release it. Only fusing the lightest few nuclei actually releases much energy.

Accretion disks are not dense enough to sustain fusion at those temperatures.

Can you please explain why the plasma density in the accretion disc can't sustain fusion?

I had the impression that the density is an outcome of a pressure.
If I understand it correctly, the fusion activity is mainly taking place at the core of the Sun due to the pressure at the core.
So, which pressure is stronger: The pressure at the accretion disc (almost at the diameter of the Schwarzschild radius of a SMBH) or at the Sun core?

Can you please explain why the plasma density is critical to sustain fusion?

I had the impression that the pressure is critical. Therefore, (If I understand it correctly), the fusion activity is mainly taking place at the core of the Sun.
So, which pressure is stronger: The pressure at the accretion disc (almost at the diameter of the Schwarzschild radius of a SMBH) or at the Sun core?

The important factors in the rate of fusion are the energy (temperature) of the particles (which allows them to overcome the electrostatic barrier to fusion) and the number of interactions (which is related to the number of particles, hence density), which makes it more likely you will get enough interactions to make the rare ones that lead to fusion common enough to make the whole chain viable.

Note that the accretion disk doesn't really extend to the Schwarzschild radius - there is a last stable orbit at three or more times this value. Below that material is infalling.

As for which system has the greater density - I am fairly sure it is the solar core but I am not going to lie and claim authority on this. I couldn't find a good source for that from a quick search, the closest I found was a Reddit where someone said they had plugged numbers into the standard ADAF and thin disk models and got densities at least a billion times less than the solar core. But I have not checked their maths. If you want to the equations you need are in the paper I provided or on Scholarpedia.

The closest to fusion I could find as an accretion disk process was in the outflow from it. There a number of r-processes happen leading to nucleosynthesis, but this is just adding neutrons to elements, not pp cycle fusion.

Also - I am not a plasma physics or black hole expert. This is based on my rather basic understanding of them. Happy if someone who knows more on this wants to chime in and correct me.

Three times of this value means that:
The minimal inner most radius of the accretion disc is about 1 Light year.
Do you agree with that?
If so, can you please estimate the Outer radius value in the accretion disc and the total plasma mass?

The Milky Way is not a black hole, and does not have a Schwarzschild Radius. Raj was misleading.

To be fair, he does say "would be" (ie. if it were a black hole).

The same link does have a value for the radius of the black hole: "the supermassive black hole at the center of the Milky Way has a mass of about 4 million solar masses, and thus a Schwarzschild radius of 12 million kilometers" (I haven't checked if it is correct or not)

"the supermassive black hole at the center of the Milky Way has a mass of about 4 million solar masses, and thus a Schwarzschild radius of 12 million kilometers. That is less than 10% of the Earth-Sun distance (150 million km)."

"Plasma is not something that plays a role in fusion as if it were a tool or an instrument for its achievement. It is instead the only possible medium where nuclear fusion can occur: very basically, high enough temperature for protons to overcome the Coulomb repulsion, and high enough density for increased chances of fusion reactions.

So it is an intimate part of nuclear fusion, rather than an appendix or a component of it. All components of nuclear fusion rather revolve around the plasma: how to heat it, how to contain it, how to shape it, how to control it, etc."

"The two beams, or jets, were revealed by NASA's Fermi space telescope. They extend from the galactic center to a distance of 27,000 light-years above and below the galactic plane."

"The jets were produced when plasma squirted out from the galactic center, following a corkscrew-like magnetic field that kept it tightly focused. The gamma-ray bubbles likely were created by a "wind" of hot matter blowing outward from the black hole's accretion disk. As a result, they are much broader than the narrow jets."

"Finkbeiner estimates that a molecular cloud weighing about 10,000 times as much as the Sun would be required."
"Shoving 10,000 suns into the black hole at once would do the trick. Black holes are messy eaters, so some of that material would spew out and power the jets,"

It is stated: "The jets were produced when plasma squirted out from the galactic center", but in reality they see: "a "wind" of hot matter blowing outward from the black hole's accretion disk." However, they also claim that this hot matter had set a molecular cloud .

Why the plasma which had been squirted out had been first converted into "Hot matter" blowing out and latter on set molecular cloud?
How could it be that a plasma from the accretion disc can set molecular cloud without fusion activity?

If I remember correctly, the total mass in the accretion disc is estimated as less than one sun mass.
So, how could it set a steady stream of jet with estimated 10,000 total Sun mass?
It is stated: "Shoving 10,000 suns into the black hole at once would do the trick", but how can we fit 10,000 sun mass in the accretion disc at once?
Do we see any accretion disc with estimated mass of 10,000 sun mass "at once"?
If I understand it correctly, in all of our observations we only see a stream of hot mass blowing away from the accretion disc.
Did we find even one evidence for any sort of external mass which is moving in the accretion disc?
How the accretion disc can blow out a steady stream of jet without getting in new mass constantly?
What is the source for this constant mass in the accretion disc?

Why the plasma which had been squirted out had been first converted into "Hot matter" blowing out and latter on set molecular cloud?

It is a pop-sci article. Expect terminological inexactitude. See https://arxiv.org'pdf/1802.03890.pdf for a summary of thecurrent possible models for the creation of these structures. There are a few contenders, although the leptonic jet one seems strongest at the moment.

Originally Posted by Dave Lee

How could it be that a plasma from the accretion disc can set molecular cloud without fusion activity?

*The molecular cloud was what was hypothesised to have interacted with the accretion disk to fuel the AGN-like burst of activity. The Fermi bubbles are not molecular clouds. If that is what you are asking, I am not 100% sure I follow your question.

Originally Posted by Dave Lee

If I remember correctly, the total mass in the accretion disc is estimated as less than one sun mass.

Do you have a reference for that? I couldn't find any numbers easily.

Originally Posted by Dave Lee

So, how could it set a steady stream of jet with estimated 10,000 total Sun mass?

Even if that were its mass - it didn't. Something that size is proposed to have fallen into the system, triggering the energetic events that created the bubbles.

Originally Posted by Dave Lee

It is stated: "Shoving 10,000 suns into the black hole at once would do the trick", but how can we fit 0,000 sun mass in the accretion disc at once?

Pop-sci again. Imprecise language. The hypothesis is that an object of that mass fell in and the resultant interactions resulted in the Fermi bubbles.

Originally Posted by Dave Lee

Do we see any accretion disc with estimated mass of 10,000 sun mass "at once"?

The only accretion disks that function in this mass range are SMBH ones. Given that we can only study one of them in detail it is not a shock to have to infer properties of others from more indirect observations.

Originally Posted by Dave Lee

If I understand it correctly, in all of our observations we only see a stream of hot mass blowing away fromtheaccretion disc.

We see a range of effects. Winds, Jets, Outflows, Flares.

Originally Posted by Dave Lee

Did we find even one evidence for any sort of external mass which is moving in the accretion disc?

What do you mean by this? Do you mean do we see evidence for material being incorporated into an accretion disk? Yes, we do. We see gas tails from G1 and G2 consistent with gravitational disruption and matter being dragged off.

Originally Posted by Dave Lee

How the accretion disc can blow out a steady stream of jet without getting in new mass constantly?

What exactly are you asking about? Jets? Winds? The accretion disk is getting new material, but the one in SagA is not getting much which is partly why the centre is pretty quiescent.

Originally Posted by Dave Lee

What is the source for this constant mass in the accretion disc?

It isn't constant mass, it varies depending on what has interacted with it and what material has been added to it. There is plenty of material in the galactic centre.

What do you mean by this? Do you mean do we see evidence for material being incorporated into an accretion disk? Yes, we do. We see gas tails from G1 and G2 consistent with gravitational disruption and matter being dragged off.

Please be aware that I only focus on the core of spiral galaxy.
Are G1 and G2 accretions in the core of Spiral galaxies?

We only focus on the accretion disc of the SMBH in the center of spiral galaxy.
If those gas clouds are drifting into the accretion disc of the Milky Way, than it is relevant.
However, the activity inside a gas cloud, (even if it is located very close to the SMBH) isn't relevant to our discussion.

If those gas clouds are drifting into the accretion disc of the Milky Way, than it is relevant.
However, the activity inside a gas cloud, (even if it is located very close to the SMBH) isn't relevant to our discussion.

Large streamers of gas being stripped off nearby gas clouds and pulled towards the accretion disk are, however, relevant.